New reports of somatic chromosome number and symmetric or asymmetric karyotype estimation of Sechium edule (Jacq.) Sw. (Cucurbitaceae)

Abstract

Sechium edule (Jacq.) Sw. distributed well in Eastern Himalayan region, fourteen genotypes collected randomly from Kigwema village, Kohima (Nagaland) at an average altitude of 1538 masl (meter above sea level) with 25.61°N latitude and 94.35°E longitudes. Somatic chromosome numbers are diploid in nature. Chromosome numbers are in agreement and comparable with earlier reports except 2n=2x=22. The chromosome number 2n=2x=22 could not be traced out in the present material collected for study. Two (2) new chromosome numbers 2n=2x=32 and 2n=4x=52 were recorded and expected to be diploid and tetraploid in nature respectively. It was expected that tetraploid (2n=4x=52) number of chromosome might be originated from the earlier reports of diploid chromosome number 2n=2x=26. Both chromosome numbers 2n=2x=32 and 2n=4x=52 are reported for the first time by the authors in the present study. Range of chromosome length was recorded in between 0.501 – 1.343. The range of chromosome length are in agreement with earlier reports of 0.700 – 0.900 approximately. Range of chromosome length suggested minute (<1µm) and small (1-3µm) size of chromosomes with small differences and variations in chromosome length (CV_CL). Inter-chromosomal indices (A₂ and Rec), intra-chromosomal index (particularly, Stebbin’s classification) and both inter and intra chromosomal indices (DI and GI) estimated symmetric nature of the karyotype.